Tristan Croll added the comment:
I've cross-posted the following to the SWIG bug tracker. Hopefully someone can
find an answer, because I'm getting nowhere.
If I have two classes Foo and Bar (where Bar has a function get_foo() that
returns a Foo object) defined in the SWIG-generated library foobar, and wrap
them as follows:
```
def mappedclass(old_cls):
'''
Ensures that objects returned from functions in the clipper_core
library are instantiated in Python as the derived class with the
extra functionality.
'''
def decorator(cls):
def __newnew__(thiscls, *args, **kwargs):
if thiscls == old_cls:
return object.__new__(cls)
return object.__new__(thiscls)
old_cls.__new__ = __newnew__
return cls
return decorator
@mappedclass(foobar.Foo)
class Foo(foobar.Foo):
pass
@mappedclass(foobar.Bar)
class Bar(foobar.Bar):
def get_foo(self):
return super(Bar, self).get_foo()
```
then in Python 3.5:
```
f = Foo()
b = Bar()
b.get_foo()
```
all work. In Python 3.6:
```
f = Foo()
b = Bar()
```
... both work, but
`b.get_foo()`
yields the error as per my OP. Real-world examples:
Constructor (works without trouble in both versions)
```
SWIGINTERN PyObject *_wrap_new_Cell_descr__SWIG_0(PyObject
*SWIGUNUSEDPARM(self), PyObject *args) {
PyObject *resultobj = 0;
clipper::Cell_descr *result = 0 ;
if(!PyArg_UnpackTuple(args,(char *)"new_Cell_descr",0,0)) SWIG_fail;
{
try
{
result = (clipper::Cell_descr *)new clipper::Cell_descr();
} catch (clipper::Message_fatal m)
{
SWIG_exception(SWIG_RuntimeError, m.text().c_str() );
SWIG_fail;
} catch (std::out_of_range e)
{
const char *errString;
if ( !strcmp(e.what(), "" ) ) {
errString = "Index out of range!";
} else {
errString = e.what();
}
SWIG_exception(SWIG_IndexError, errString );
SWIG_fail;
} catch (std::length_error e)
{
SWIG_exception(SWIG_ValueError, e.what() );
SWIG_fail;
} catch (std::invalid_argument e)
{
SWIG_exception(SWIG_ValueError, e.what() );
SWIG_fail;
} catch (std::exception e)
{
SWIG_exception(SWIG_UnknownError, e.what() );
SWIG_fail;
} catch (...)
{
SWIG_exception(SWIG_UnknownError, "Unknown error" );
SWIG_fail;
}
}
resultobj = SWIG_NewPointerObj(SWIG_as_voidptr(result),
SWIGTYPE_p_clipper__Cell_descr, SWIG_POINTER_NEW | 0 );
return resultobj;
fail:
return NULL;
}
```
Getter (fails under the above conditions):
```
SWIGINTERN PyObject *_wrap_Cell_cell_descr(PyObject *SWIGUNUSEDPARM(self),
PyObject *args) {
PyObject *resultobj = 0;
clipper::Cell *arg1 = (clipper::Cell *) 0 ;
void *argp1 = 0 ;
int res1 = 0 ;
PyObject * obj0 = 0 ;
clipper::Cell_descr result;
if(!PyArg_UnpackTuple(args,(char *)"Cell_cell_descr",1,1,&obj0)) SWIG_fail;
res1 = SWIG_ConvertPtr(obj0, &argp1,SWIGTYPE_p_clipper__Cell, 0 | 0 );
if (!SWIG_IsOK(res1)) {
SWIG_exception_fail(SWIG_ArgError(res1), "in method '" "Cell_cell_descr"
"', argument " "1"" of type '" "clipper::Cell *""'");
}
arg1 = reinterpret_cast< clipper::Cell * >(argp1);
{
try
{
result = clipper_Cell_cell_descr(arg1);
} catch (clipper::Message_fatal m)
{
SWIG_exception(SWIG_RuntimeError, m.text().c_str() );
SWIG_fail;
} catch (std::out_of_range e)
{
const char *errString;
if ( !strcmp(e.what(), "" ) ) {
errString = "Index out of range!";
} else {
errString = e.what();
}
SWIG_exception(SWIG_IndexError, errString );
SWIG_fail;
} catch (std::length_error e)
{
SWIG_exception(SWIG_ValueError, e.what() );
SWIG_fail;
} catch (std::invalid_argument e)
{
SWIG_exception(SWIG_ValueError, e.what() );
SWIG_fail;
} catch (std::exception e)
{
SWIG_exception(SWIG_UnknownError, e.what() );
SWIG_fail;
} catch (...)
{
SWIG_exception(SWIG_UnknownError, "Unknown error" );
SWIG_fail;
}
}
resultobj = SWIG_NewPointerObj((new clipper::Cell_descr(static_cast< const
clipper::Cell_descr& >(result))), SWIGTYPE_p_clipper__Cell_descr,
SWIG_POINTER_OWN | 0 );
return resultobj;
fail:
return NULL;
}
```
----------
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue29758>
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